1. Field of the Invention
The present invention relates to telephone networks and, in particular but not exclusively, telephone networks for mobile telephone systems.
2. Description of the Prior Art
The structure of telephone networks employing third generation internet protocol industrial focus group architecture (3G IP) and third generation partnership project architecture (3G PP) is such that any voice internet protocol traffic (VoIP) goes through a fairly lengthy route within the network. Thus, for example as shown in FIG. 1, VoIP traffic originating at a mobile station (T1) 2 and destined for a target station (T2) 14 takes the following route; starting from the mobile station 2, traffic is passed by a radio network controller (RNC) 4 to a serving GPRS (general packet radio system) support mode SGSN 6. From there the signal is passed by a gateway GPRS support node (GGSN) 8 to a media gateway (MGW) 12, when a public switch telephone network (PSTN) is met or when transcoding is required, following which the destination of the target telephone (T2) 14 is reached.
The traffic handling using the path as outlined above can be very inefficient.
So far there is no co-ordination between choice of GGSN and VoIP media gateway (MGW). The determination of GGSN (when setting up PDP bearer) and choice of MGW (determined by application level call control) are two independent procedures. However, as the traffic has to pass these two points, the determined GGSN and MGW can result in a less than optimum traffic route. For example, this would happen when the mobile station (MS) GGSN and MGW form a triangle.
In the public land mobile network (PLMN) (eg the mobile telephone operators network) traffic has to pass through a first interface Iu-ps between the RNC 4 and the SGSN 6, a second interface Gn between the SGSN 6 and the GGSN 8. As a result, the user packet acquired the following protocol headers or series of codes; real time transport protocol/user datagrams protocol/internet protocol/GPRS tunnelling protocol/user data gram protocol/internet protocol/L1, 2 (RTP/UDP/IP/GTP/UDP/IP/L1,2). The result is that for real time or voice message, the resource usage is low (about 25%).
It is an object of the present invention to provide an improved network architecture.